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The onset of colder than normal weather always brings up the question of how the cold will affect insect populations in the upcoming year. Though the answer to this question seems simple it is actually complex.

Basically insects can seek shelter from the cold and they can produce compounds in their bodies that are very similar to the antifreeze that we put in our cars. These compounds keep them from freezing solid. It is not the cold but the freezing/thawing processes that usually causes insect death.

When thinking about how winter affects insects we need to remember that we are talking about population size. An individual insect is either alive or dead, there is no in between. But an insect population, a group of insects, can have different rates of survival. So, in a “mild winter, perhaps 10% of the overwintering insects die leaving 90% of them to live into the spring. On the other hand, in a “hard winter, perhaps 80% of the population will die leaving only 20% of the population to survive into the spring.

Remember that snow and ice are insulators. Though what they coat will be at freezing (32 F) and temperature will drop slowly, this is often much better than the air temperatures from an arctic blast! So, for example, when there is a -10 F day, things that are covered with snow and ice will remain much nearer to 32 F, providing a measure of protection from the ultra-cold temperatures.

Erfan Vafaie who is an integrated pest management specialist at Texas A& M had this to say, generally speaking, insects have three main strategies for dealing with the cold: freeze tolerance, freeze avoidance and migration. With freeze tolerance, “typically, certain environmental cues are involved. For example, shorter days and cooling temperatures may induce mechanisms that help the insect tolerate freezing,” Vafaie said. “When the weather warms back up, they thaw and become active again.”

Other insects cannot tolerate freezing, but have other mechanisms to prevent ice formation in their cells, he said. “We call 32 Fahrenheit the freezing point of water, but the temperature at which ice forms depends on the content of the solution,” Vafaie said. “For example, saltwater at a concentration of 23.3 percent may not freeze until the temperature is minus 6 degrees Fahrenheit. In the same way, some insects use certain compounds called ‘cryoprotectants,’ similar to the ethylene glycol found in our car’s antifreeze, that lower the temperature at which freezing occurs. This helps them survive at subfreezing temperatures.”

The third strategy, migration is also commonly used by some insect species. Perhaps the best known is the Monarch butterfly which migrate to Mexico and Southern California every winter.

One thing that may defeat many of these survival strategies, however, is when there are multiple incidences of very cold weather with warm temperatures in between. Such rollercoaster weather can decrease insect survival orreproductive potential, according to Vafaie.

All insects have some ability to withstand cold weather. One of the most common strategies is to bury themselves underground, beneath leaf litter, or to burrow under tree bark for protection and hibernate for the season. These protective maneuvers work pretty well most winters, allowing insect populations to remain relatively stable.

A recent spate of warmer than average winters over the last few decades, however, has allowed the populations of some types of creepy crawlies to explode. When winter temperatures never reach a truly deep freeze, bugs make it through to spring unscathed and ready to multiply.

For instance, Lyme-disease-carrying deer ticks — which are not actually insects, but eight-legged arachnids, like spiders — are now seen in larger quantities and have spread farther to the north than they once roamed.

Fleas are a year-round nuisance, but they can die off outside when outside temperatures dip below freezing. In fact, once the temperatures fall to 37 degrees F, it’s cold enough to kill mature fleas as well as eggs, larvae and pupae. But those temps need to be sustained for 10 days or longer. And that’s outside.

Inside the home, however, where it’s nice and toasty warm, fleas survive all winter long no matter what the temperature is outdoors. Often times, the pupae can go dormant in cool areas like basements or crevices in the home, then re-infest once the temperatures warm up again. You may need to treat pets year-round, if you had an infestation late summer or in the fall.

The following increase mortality of overwintering insects:

• cold, wet weather, particularly with wet but not frozen soils for insects overwintering in the ground, and lack of snow or ice cover will cause the greatest or at least the most common decrease in survival of overwintering insects.
• Extreme cold that is not moderated by snow or ice cover increases mortality but is a rather rare event.
• Repeated wide swings in temperature, alternating warm and cold during the traditionally cold months (e.g. Dec – Mar).
• A long, warm period late in the traditionally cold season followed by a quick return to very cold conditions.

 

SOURCES:
• Winter weather effects on insect populations Ag Professional March 5, 2015
• Many insect pests have survival strategies for cold weather January 21, 2014 Writer: Robert Burns, 903-834-6191, rd-burns@tamu.edu Contact: Erfan Vafaie, 903-834-6191, Erfan.Vafaie@ag.tamu.edu
• Natural Ways To Combat Fleas! by Amber Kanuckel | Monday, May 25th, 2015 Home and Garden /Farmer’s Almanac